1. Field of the Invention
The present invention relates generally to detecting systems and, more particularly, to a radioactivity detection system and detectors therefor.
2. The Prior Art
Various types of radioactivity distribution measurement systems are known in the art for determining the location of radioactive material injected in diagnostic amounts into a human body or the like. These systems utilize an array of scintillators for sensing radioactive events within the body and a plurality of photomultiplier tubes that are coupled to the scintillators for detecting the sensed events. The address location for each activated scintillator is linearly encoded and then processed to provide a pictorial representation of the relative radioactive event levels detected by the scintillators. Spatial resolution is limited by the smallest diameter of available photomultiplier tubes.
Such systems have suffered from the disadvantages that linear encoding of scintillator address locations requires an excessive number of photomultiplier tubes in order to provide each scintillator with a unique address location. A large number of photomultiplier tubes increases the system costs and increases the likelihood for system downtime. Such systems also suffer from the disadvantage that the dark current of the photomultiplier tubes causes pulses (dark noise) which, in certain instances, are incorrectly interpreted as valid scintillations.
In U.S. Pat. No. 4,267,452, assigned to a common assignee, a system is disclosed in which three photomultiplier tubes are required to determine the position of an activated scintillator. This system shows one photomultiplier tube superposed on four crystal assemblies, with each assembly containing four scintillators. There are thus sixteen scintillators that potentially can provide light signals, in various amounts, to one photomultiplier tube. This in turn requires a rather complex anticoincidence/coincidence logic in the processing of the signals from the photomultiplier tubes.